Two studies published in Health Affairs suggest that soda taxes have mixed results. Shirley S. Wang of the WSJ Health Blog summarizes the studies:

One study led by a Rand Corp. researcher examined children’s body mass index and consumption of sugar-sweetened drinks in a national sample of more 7,000 elementary-school students between 1998 and 2004. The majority of the kids lived in states where sodas were taxed more than other foods, with levies on sodas ranging as high as 7%.

The results showed no overall difference in beverage consumption in states that taxed sodas more, but there was some benefit for some groups including kids who started off heavier, those from low-income families, African Americans and those who watched a lot of TV. There was some evidence that a higher tax was linked to lower body mass index in third- to fifth-graders.

“To have a measurable effect on consumption, taxes need to be tied to consumption, and they need to be larger than the existing state variation in sales taxes,” the study authors concluded.

The second study, looking at another national sample of kids, found “little difference” in the body mass indexes of kids who live in states with a soda tax compared with states without one. They also found that fifth through eighth graders drank less sodas at school when vending machine access was limited.

“This finding of little consumer response to soft drink taxes in reducing consumption could be partially explained if consumers do not react to the small, and often hidden, tax rates typically applied to soft drinks,” according to the researchers led by a Yale prof.

Earlier studies have found have found that taxing sugary sodas just a penny an ounce would decrease consumption significantly. A recent study suggest that 10% increase in price leads to an 8% reduction in consumption.